368 PALAEONTOLOGY OF ILLINOIS. 







DELTODUS ANGUSTUS, N. and W. 



PI. iii, fig. 7. 



TOOTH narrowly triangular in outline, about one inch in ex- 

 treme length by one-quarter inch in breadth at widest part; 

 under surface nearly flat ; upper face coarsely punctate and 

 raised by a strong but obtuse ridge which borders the longer 

 margin, running from the narrower nearly to the broader end, 

 where it gradually slopes down to the edge. Parallel with the 

 margin of the tooth, opposite the ridge, is a broad, shallow 

 furrow, which runs from the narrower to the broader end. 



This tooth is much smaller and relatively narrower than any other species of 

 the genus hitherto described. In its general aspect it is most like D. rhomboi- 

 deus, N. and W. (Geol. Survey Illinois, vol. 2, p. 100, pi. ix, fig. 8), but is very 

 much narrower and has but a single ridge, while D. rhomboideus may be said 

 to have three ridges crossing the crown longitudinally. 



Formation and locality : Chester group ; Chester, Illinois. 



DELTODUS ALATUS, N. and W. 



PI. ii, fig. 6. 



TEETH of medium or large size, thick and massive, broadly 

 triangular in outline, strongly arched in both directions, crown 

 mainly composed of one high and broad arched ridge extend- 

 ing from the acute angle to the opposite side, bordered on the 

 shorter side of the triangle by a relatively broad, low margin 

 or wing ; bony base of the tooth prolonged, in a wing-like ex- 

 pansion from the broad, rounded extremity of the crown ridge; 

 enamel surface all coarsely granulo-punctate. 



This species has much in common with D. spatulatus (vol. 2, p. 100, pi. 14, 

 fig. 7), but the wing-like expansions of the crown and base, referred to in the 

 description given, have not been noticed in any specimens yet found of that 

 species, which also comes from a different horizon, the Burlington limestone, 

 where nearly all the species are distinct from those accompanying the fossil 

 under consideration. A beach-worn tooth, from which the margin had been 



